Electric lamp



April 23, 1935. E. FRIEDERICH ELECTRIC LAMP Filed March 14, 1955 fAZI ENTUR EAAZET FBIEDERJZJH W (Z/6&4,

4 .5 25 ATTURNEY' gas-vii Patented Apr. 23, 1935 UNITED STATES ELECTRIC LAMP Ernst Friederich, Berlin-Charlottenburg, Germany, assignor to General Electric Company, a corporation of New York Application March 14, 1933, Serial No. 660,701 In Germany March 24, 1932 4 Claims. (Cl. 176-1) My invention relates to electric lamps and comprises a lamp in which light is produced by a bombardment of electrons on an anode. Light has been produced by electronic bombardment on "an anode consisting of a material of high heat resistivity from either a so-called cold cathode or a cathode which is directly heated by the passage of current therethrough. Up to the present time these methods have been very unsatisfactory because with cold cathodes exceedingly high voltages were required, and with directly heated cathodes the electron current was distributed non-uniformly in the lamp as a result of the voltage drop along the cathode, thus causing a one-sided overload of both electrodes.

According to my invention, the above disadvantages are obviated by using an indirectly heated glow cathode for producing the electrons, because such a cathode has a uniform voltage over its entire surface, thereby producing a veryuniform electrode current. With an indirectly heated cathode the lighted anode body may be so constructed that the space charge will be reduced to such an extent that the lamps may be operated at the customary incandescent lamp voltages. The lighted anode may, for example, comprise a wire which is wound to form a cylindrical, conical or spherical surface surrounding the cathode. Indirectly heated cathodes surrounded by an anode have been utilized in electron tubes for amplifying and rectifying purposes. However, since the current load of such tubes is very small and the surface of the anode, which usually comprises a cylindrical sheet, 'is very large by comparison, the anode is not noticeably heated by the electron current, whereas the aniode of my device is heated to a glowing temperaure.

When insulating supports are used for the lighted anode body, said body will be more intensively heated in the portion adjacent the leading-in wire. This may be compensated for by giving the anode body a special shape such as conical, or by decreasing the density of the electron bombardment at those points which are adjacent the leading-in wires by providing extra windings of said anode body when it is helical in shape. Generally, however, it is better to design the lighted anode bod-y as an equipotential electrode so that the voltage drop will take place in the vacuum space in the electron path.

The new electric lamp can be operated without a series resistance or other switching devices just like an ordinary incandescent lamp. The consumption ofthe lamp at a given line voltage depends solely on the magnitude of heating current. In manufacturing different sizes of lamps only the surface is the determining factor and not the shape of the luminous anode body.

An advantage of the new lamps over the conventional incandescent lamp which is heated by resistance is that heavier wires may be used. It is known that the life of the tungsten filament lamp depends to a great extent on the thickness of the filament. Thinner places in the filament are heated more intensively by the current than adjacent portions, thus leading to an early burnout. On the other hand, in the new lamp thin parts of the lighted anode body will not be overheated, but will be spared because of the more intensive space charge at those points. Further, in the new lamp the evaporated tungsten is moved in the path of the electron current and is deposited at points which do not interfere with the light radiation, namely, the electrodes, while in the conventional incandescent lamp the evaporated tungsten is deposited on the walls of the bulb and causes blackening thereof.

In the drawing is shown a form of lamp structure comprising my invention in which Fig. 1 is a partially sectioned elevation of an indirectly heated cathode; Fig. 2 is an elevation of the internal structure of the lamp; and Fig. 3 is a partially diagrammatic representation of the internal structure of the lamp in which a grid is located between the cathode and anode.

Referring to Fig. 1, the cathode comprises a small insulating tube [0 of magnesia, aluminum oxide, or similar material, constituting the core of said cathode. 'Said tube I0 is providedwith several holes H in which are located a coiled heating wire B2. The protruding portions of the heater B2 are provided with an insulating cover I I3. 0n the outer surface of tube I0 is provided a metallic covering 14, preferably nickel, to which a lead wire I5 is connected. On the surface of the metallic covering I4 is provided a layer It of an electron emitting material such as barium oxide.

Referring to Fig. 2, four leading-in wires I1, l8, l9 and 20 are sealed in a stem press 2|. The two lead wires l1, l8 are connected to the positive terminal of the lamp base, while the lead wires i9, 20 are connected to the negative terminal. A helically coiled anode wire 22 surrounds the indirectly heated cathode Ill-l6 and is mounted on a support 23 which is mounted on the leadingin wire ll. By means of the support wire 23 the individual turns of the anode wire 22 are connected together and brought to the same potential. The ends of the heating wire l2 are connected to the ends of the leading-in wires l8, l9, while the wire l5 from the metallic coverin I4 is connected to' the leading-in wire 20. Since the electron current also strikes the support wire 23, and .the leading-in wires, a portion of the heating energy is lost. This loss may be prevented by coating those portions with a nonconducting material. The above described elements are, of course, enclosed in a glass bulb which is not shown.

A grid 24 (Fig. 3) may advantageously be provided between the anode and cathode in order to control or limit the passage of the current. Said grid may be given a certain voltage by connecting it through its lead 25 to a certain part of the heater of the cathode through the medium of an adjustable high resistance 26 which is connected across the terminals of the lamp. The grid may also be given a negative voltage if the voltage for the discharge current is taken from a point on the heater such as at the center thereof.

When comparatively small anodes are heated it may be to advantage to reduce the space charge in order to obtain a sufliciently high current at low voltage. This may be done by providing in the bulb a small quantity of gas or vapor, preferably mercury vapor at a pressure of approximately 01 mm. or less.

The anode may comprise a material having the property of selective radiation, such as aluminum oxide or oxides of rare earths or mixtures thereof. Such materials are either sufiiciently conductive to carry current at the temperature at which they are used, especially when they are deposited in thin layers on conductors such as tungsten, or they may be made sufliciently conductive by adding other materials.

*1 The light intensityof the lamp may be further improved if the scattered electrons present in the bulb are utilized for the excitation of fluorescent coatings in said bulb. Said coatings may consist of zinc silicate or calcium tungstate.

What I claim as new and desire to secure by Letters Patent of the United States is:-

1. An electric lamp comprising a bulb, an electron source in said bulb comprising an indirectly heated cathode and an incandescible anode which is heated to incandescence by electron bombardment from said cathode, said anode comprising a wire structure of small surface area surrounding said cathode.

2. An electric lamp comprising a bulb, an electron source in said bulb comprising an indirectly heated cathode and an incandescible anode which is heated to incandescence by electron bombardment from said cathode, said anode comprising an equipotential wire structure of small surface area surrounding said cathode.

3. An electric lamp comprising a bulb, an electron source in said bulb comprising an indirectly heated cathode, an incandescible anode of small surface area which is heated to incandescence by electron bombardment from said cathode, and a grid electrode disposed between said cathode and anode.

4. An electric lamp comprising a bulb, an electron source in said bulb comprising an indirectly heated cathode and an incandescible anode which is heated to incandescence by electron bombardment from said cathode, said anode comprising a coiled filament surrounding said cathodel ERNST FRIEDERICH. 

